After two decades of effort to devise satisfactory contraceptive methods which depend on metabolic control mechanisms (oral contraceptives and progestational inserts) or on intra-uterine mechanical disruption i.e. intra-uterine devices (IUD's); alternative methods which depend on barriers (diaphragms, condoms) and on topical application of spermicides or other contraceptives (intravaginal foams or suppositories) have not become obsolete, and are still in wide use. These methods attract considerable interest due to their safety, freedom from undesirable side effects, and relative accessibility, without the need for a physician's intervention. The present invention relates to compositions for, and methods of, contraception based on topical intravaginal application of spermicides or other antifertility agents which inhibit sperm function.
Present formulations for intravaginal application of sperm function inhibitors are designed to insure coverage of the entire vaginal vault with the active ingredient (usually a surfactant, and typically nonoxynol-9, a non-ionic surfactant).
Thus, while the form of application of the spermicide may be varied, such as, gel, foam, cream, or a suppository designed to disintegrate and spread by means of, for example, an effervescent dissolution process, all of these application methods are basically similar to barrier methods in that they depend in the final analysis, on encountering and destroying all sperm which enter the vagina.
For this reason, the present formulations cannot be considered totally satisfactory solutions to the problem. If they succeed in coverage of the entire vaginal surface, they are inherently messy and unaesthetic. If they fail to do so, they are relatively ineffective; a particular problem with those formulations designed in the form of dissolving suppositories.
Compositions using poloxamers which enhance absorption of drugs by certain mucus membranes have been previously disclosed. See U.S. Pat. Nos. 4,100,271 and 4,188,373. These compositions have been directed toward treatment of eye disorders, and have been designed specifically for application to the surface of the eye. They contain a substantial percentage of a polyoxyethylene--polyoxypropylene block copolymer of average molecular weight 5,000-15,000, a "poloxamer," commonly sold under the trade name Pluronic.
It has now been found that compositions designed for intravaginal application containing poloxamers in substantial amount, have unexpected inherent spermicidal properties, and are uniquely suitable for effective delivery of anti-spermatozoal agents to intercept sperm otherwise destined to penetrate the cervical mucus.